UPDATE 2017-04-02: https://twitter.com/anholt/status/840753745721937920 there might be a working driver now...

UPDATE: Latest OpenGL work status seems to be here, https://dri.freedesktop.org/wiki/VC4/ which is Required for Webkit2.

Since creating a Webconverger Rpi2 port based upon Archlinux-Arm (Alarm) I've run into the issue whereby Webkit2 stops working after an upgrade.

The canonical issue is raised upon https://bugs.webkit.org/show_bug.cgi?id=143817, since the Alarm project say its an upstream issue.

THE MISSION: Get Webkit2 working on the Alarm Rpi2!

Rpi2

Does Webkit2 work on Raspbian? Yes... but without hardware acceleration for compositing

So upon Webkit2 the Stable tarball is WebKitGTK+ 2.10.3. Alarm's webkit2gtk is good at being current, however Debian's packaging is a bit odd.

Firstly their package is called libwebkitgtk-3.0-0. The source package from where it is built from is confusingly called webkitgtk and their current version at time of writing is 2.4.8-2+rpi1, which is about 6 months old.

After grabbing the source, you can see a scary amount of patches. 314 to be exact.

pi@raspberrypi ~/webkitgtk-2.4.1/debian/patches/rpi $ ls -1 *.patch | wc -l
314

So one of these patches probably might make Webkit2 work on ARMv7h. Well... actually I am not confident at all since I know for a fact webkit2gtk-2.6.5-1 works fine in Webconverger's Rpi2 port, and Raspbian's heavily patched version is 2.4.8... which is older!

Raspbian's libwebkit2gtk-4.0-37 and the source package webkit2gtk of version 2.9.3, which is newer than the last known Webkit2 in Alarm, 2.6.5.

Here there are thankfully only 12 patches (down from 314):

pi@raspberrypi ~/webkit2gtk-2.9.3+dfsg1/debian/patches/rpi $ ls -1
0001-GTK-Crash-performing-drag-and-drop.patch
0002-GTK-Empty-gtk-font-name-setting-causes-WebProcess-cr.patch
0003-CairoGL-should-be-checked-unconditionally.patch
0004-GTK-Forcefully-disable-gtk-doc-and-gobject-introspec.patch
0005-GTK-The-Missing-Plug-in-buttons-are-not-showing-up-o.patch
0006-GTK-Crash-when-spell-checker-returns-no-guesses.patch
0007-Fix-build-with-ENABLE-DATABASE_PROCESS-and-ENABLE-IN.patch
0008-RPI-Demote-GCC-4.9-requirement-if-ENABLE_DATABASE_PR.patch
0009-Fix-ENABLE_OPENGL-OFF-builds.patch
0010-CMake-Trigger-the-memory-reduction-tricks-on-armhf-t.patch
0011-CMake-Reduce-debug-info-on-32bit-arches-using-g1-to-.patch
0012-RPI-Disable-AC-by-default.patch

My next step now is to I have been in contact with https://www.collabora.com/.

Summary: Emanuele tells me the proprietary GL stack for the Rpi2 is not reliable enough (Webkit may stress it too much) for Webkit2.

So the work around is to build with -DENABLE_OPENGL=OFF which means no accelerated composition at all. Emanuele is working upon a software only compositor, but it's far from finished.

Workaround that breaks accelerated composition for everyone else

So the Rpi2 which is a Arm7 board differs say to the ODROID-XU4 because it uses the Broadcom VideoCore GPU instead of the ARM reference GL hardware called Mali.

Obviously a Archlinux Arm7 package for Webkit2 with -DENABLE_OPENGL=OFF would be detrimental to working GL implementations like Mali, so at this present time the Alarm package PKGBUILD is unlikely to be fixed for Rpi2! Since the fix would disable GL working acceleration for the likes of ODROID-XU4 and make them slow!

I asked Emanuele Aina about the possibility of fallback within Webkit runtime itself and not a build switch and he said there is a WebCore::Settings::setAcceleratedCompositingEnabled() setting but he has had issues with it. There needs to be a custom check, though since he works on Raspbian, he may not find time to implement it. :(

The future for Webkit on Rpi2

It doesn't look promising in the short term. Emanuele added on 2015-10-07 that it looks like one or two years from having a GL implementation we can rely on on the Broadcom based Raspberry Pi platform ! :(

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